This patch removes the autogeneration of the RAPI docs from the code
(based on docstrings) and moves the current autogenerated output to
the rapi.rst file.

The reasons behind this are multiple:
  - the build system becomes a little more simple (this could have been
	achieved also by distributing the built documentation, though)
  - it's hard to actually write documentation in docstrings; you have to
	fit restructured text inside the docstrings, and this results in
	not really nice output
  - even by being close to the code, the documentation manages to get
	out of sync (not paying attention to docstrings)

This will also help with the move to sphinx.

Signed-off-by: Iustin Pop <iustin@google.com>
Reviewed-by: Guido Trotter <ultrotter@google.com>